Simple access to tungsten-stabilized disecondary diphosphines

Article abstract of DOI:10.1021/om400637j

Transient terminal phosphinidene complexes [RP-W(CO)₅] dimerize in the presence of copper chloride, and the dimers react in situ with triphenylphosphine-borane to give the disecondary diphosphine complexes [RPH-PHR][W(CO)₅]₂. When R = CH₂CH ₂Cl, a cyclization takes place to give the diphosphirane complex. A 1,2-diphospholane is obtained for R = Ph by further reaction with 1,3-dibromopropane in the presence of aqueous K₂CO₃.

Full text of DOI:10.1021/om400637j

Note
pubs.acs.org/Organometallics
Simple Access to Tungsten-Stabilized Disecondary Diphosphines
Rongqiang Tian,*,† Yanbo Mei,† Zheng Duan,*,† and Francois Mathey*,†,‡
̧
†College of Chemistry and Molecular Engineering, International Phosphorus Laboratory, Zhengzhou University, Zhengzhou 450001,
People’s Republic of China
‡Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang Technological University, 21
Nanyang Link, Singapore 637371
S
* Supporting Information
ABSTRACT: Transient terminal phosphinidene complexes
[RP-W(CO)5] dimerize in the presence of copper chloride,
and the dimers react in situ with triphenylphosphine−borane
to give the disecondary diphosphine complexes [RPH−
PHR][W(CO)5]2. When R = CH2CH2Cl, a cyclization takes
place to give the diphosphirane complex. A 1,2-diphospholane
is obtained for R = Ph by further reaction with 1,3-
dibromopropane in the presence of aqueous K2CO3.
isecondary diphosphines have been known for a long
time1 but have not attracted a great deal of interest,
mixture of the meso and rac diastereomers that have been
described in our previous paper.3 Since copper chloride favors
the formation of diphosphene complexes6 and since bulky
diphosphenes are known to be reducible to the corresponding
diphosphines,7 it was tempting to suspect that the phosphini-
dene species only sluggishly inserts into the B−H bond at 60
°C (the insertion is normally performed at 110 °C) and prefers
to dimerize to give the diphosphene, which is then cleanly
reduced by the borane adduct. THF is absolutely necessary to
perform the reaction depicted in eq 1. The mechanism of the
reduction of PP by BH3L probably involves a nucleophilic
attack of the negative boron onto the double bond, which is
favored by THF. The probable intermediacy of the
phosphinidene dimer has been proven by replacing 1a by the
preformed diphosphene complex 46 (eq 2).
D
probably as a result of their high reactivity and difficult
handling. The most recent contribution to their synthesis relies
on the dehydrocoupling of primary phosphines by transition-
metal catalysts.2 In a recent paper, we prepared some
decacarbonyl ditungsten complexes of disecondary diphos-
phines and noticed their good stability and the possibility of
obtaining crystals for X-ray analysis.3 It was thus desirable to
devise a simple access to such species in order to fully develop
their synthetic potential. This is the subject of this report.
RESULTS AND DISCUSSION
■
In a preceding study,4 we described the insertion of terminal
phosphinidene complexes [RP−W(CO)5] into the B−H bonds
of H3B−L (L = NEt3, PPh3). The reaction was performed in
boiling toluene with the appropriate 7-phosphanorbornadiene
precursors. It is known that the generation of phosphinidenes
from such species is catalyzed by CuCl.5 Thus, we
reinvestigated this reaction in the presence of the copper
catalyst. The outcome proved to be entirely different, as shown
in eq 1.
The higher temperature (110 vs 60 °C) needed to carry out
the reduction is probably due to the initial decomplexation step
of the π bond.
Quite unexpectedly, the replacement of the triphenylphos-
phine by the triethylamine−borane adduct led to a much lower
yield of 2a together with an unstable product (eq 3).
We separately observed that both Et3N−BH3 + CuCl and
Et3N catalyze the decomposition of 2a. The triphenylphosphine
adduct was, thus, the reagent of choice for the synthesis of the
Both THF and CuCl are necessary to obtain a satisfactory
yield of the diphosphine complex 2a, which is obtained as a 1:1
Received: July 2, 2013
Published: September 12, 2013
© 2013 American Chemical Society
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Note
disecondary diphosphine complexes. We checked that the
reaction is general (eq 4).
It must be noted that 6 has already been obtained from 1d
using the naked fluoride ion as the base, although in lower
yield.8 In another series of experiments, we prepared a
diphospholane from 2a (eq 7).
The rac diastereomer of 2c was obtained in the crystalline
state and characterized by X-ray crystal structure analysis
(Figure 1). The main difference with the crystal structure of
The diphospholane 7 was obtained as a mixture of two
diastereomers. One of these was obtained in the crystalline
state and submitted to a X-ray crystal structure analysis (Figure
2). The P−P bond length is in the normal range at 2.235 Å in
spite of the ring strain (intracyclic C−P−P angles ca. 90°), the
phenyl substituents are in a quasi-trans disposition (Ph−P−P−
Ph torsion angle 173.9°), and the complexing groups are in a
staggered conformation (W−P−P−W = 78.0°). 1,2-Diphenyl-
1,2-diphospholane has already been described in the literatur-
e.2c,9 At this stage, it is clear that it is possible to develop easily a
Figure 1. X-ray crystal structure of rac-diphosphine complex 2c. Main
distances (Å) and angles (deg): W1−P1 = 2.4846(17), W2−P2 =
2.4847(18), P1−C11 = 1.817(7), P2−C15 = 1.820(9), P1−P2 =
2.248(2); P2−P1−W1 = 113.59(8), P2−P1−C11 = 104.6(5), W1−
P1−P2−W2 = 96.15, C11−P1−P2−C15 = 0.45.
rac-2a3 lies in the value of the R−P−P−R dihedral angle which
varies from 78.3° for R = Ph to 2.16° for R = 2-Th. The two
thiophene planes make an angle of 23.3°. The C11···C15
distance is 3.305 Å, suggesting a possible π−π interaction
between the two aromatic rings.
The next step was to perform a preliminary evaluation of the
synthetic potential of these diphosphine complexes. We started
with R = CH2CH2Cl in order to verify the possibility of
obtaining phosphirane derivatives (eq 5).
In addition to the normal diphosphine 2d, which is unstable
and difficult to purify, we also obtained the monocyclized
product 5 and the diphosphirane complex 6. It is possible to
perform a complete cyclization using potassium carbonate as
the base and to obtain 6 in good yield (eq 6).
Figure 2. X-ray crystal structure of one diastereomer of the 1,2-
diphospholane complex 7. Main distances (Å) and angles (deg): W1−
P1 = 2.5118(14), W2−P2 = 2.5062(14), P1−P2 = 2.235(2), P1−C11
= 1.827(5), P2−C20 = 1.820(5), P1−C17 = 1.832(5), P2−C19 =
1.836(5), C17−C18 = 1.539(8), C18−C19 = 1.538(8); C11−P1−P2
= 101.32(18), C17−P1−P2 = 91.1(2), C11−P1−C17 = 104.8(2),
C19−P2−P1 = 90.5(2).
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Note
138.85 (pseudo-t, JCP = 6.8 Hz, CH), 194.84 (pseudo-t, JCP = 2.3 Hz,
CO cis), 196.83 (pseudo-t, JCP = 13.4 Hz, CO trans).
sizable synthetic chemistry from these disecondary diphosphine
complexes.
HRMS: calcd for C18H7O10P2S2W2 [M − H]− 876.7975, found
876.7979.
EXPERIMENTAL SECTION
Diphosphine 2d. A solution of 7-phosphanorbornadiene complex
1d (2.56 g, 4 mmol), borane−triphenylphosphine complex (2.2 g, 8
mmol), and CuCl (156 mg, 1.6 mmol) in THF was stirred at 60 °C for
4 h. After evaporation, the residue was purified by chromatography
with petroleum ether/dichloromethane (10/1) as the eluent. Yield:
compound 2d, 172 mg, 10%; compound 5, 176 mg, 11%; compound
6, 320 mg, 21%. Compound 6 has already been described.8
■
All reactions were performed under nitrogen using solvents dried by
standard methods. NMR spectra were obtained using a Bruker AV300
spectrometer. All spectra were recorded at 298 K in CDCl3. All
coupling constants (J values) are reported in hertz (Hz). Chemical
shifts are expressed in parts per million (ppm) downfield from internal
TMS. HRMS spectra were obtained on an Agilent 1290-6540 UHPLC
Q-Tof HR-MS spectrometer. X-ray crystallographic analyses were
performed on an Oxford diffraction Gemini E diffractometer. Silica gel
(200−300 mesh) was used for the chromatographic separations. The
7-phosphanorbornadiene complexes 1a−d were prepared according to
literature methods.6,10,11 Commercially available reagents were used
without further purification.
Compound 2d (Two Isomers). 31P NMR (CDCl3): δ −59.2 (1JPW
=
156.4 Hz, JPW = 72.7 Hz, JPH = 325.4 Hz), −66.1 (1JPW = 159.2 Hz,
2JPW = 72.6 Hz, JPH = 341.1 Hz). 1H NMR (CDCl3): δ 2.48−2.91 (dm,
4H, PCH2), 3.79−3.98 (m, 4H, CH2Cl), 4.98−6.86 (dm, 1JHP = 327.6
Hz, 1JHP = 344.0 Hz, 2H, PH). 13C NMR (CDCl3): δ 32.09 (pseudo-t,
JCP = 22.4 Hz, PCH2), 30.15 (pseudo-t, JCP = 28.6 Hz, PCH2), 41.10
(s, CH2), 40.91 (s, CH2,), 194.60 (pseudo-t, JCP = 4.3 Hz, CO cis,),
194.45 (pseudo-t, JCP = 4.5 Hz, CO cis,), 195.5−196.1 (m, CO trans).
2
Diphosphine 2a. A solution of 7-phenyl-7-phosphanorbornadiene
complex 1a (328 mg, 0.5 mmol), borane−triphenylphosphine complex
(276 mg, 1 mmol), and CuCl (20 mg, 0.2 mmol) in THF (10 mL) was
stirred at 60 °C for 8.5 h. After evaporation, the residue was
chromatographed on silica gel using a 10/1 petroleum ether/
Compound 5. 31P NMR (CDCl3): δ −33.0 (JPP = 193.8 Hz, JPW
=
230.7 Hz), −212.4 (JPP = 194.0 Hz, JPW = 249.2 Hz). 1H NMR
(CDCl3): δ 1.59−2.04 (m, 4H, CH2), 2.62 (dm, JHP = 60.0 Hz, 2H,
1
dichloromethane mixture, to give a yellowish solid (96.3 mg, 45%).
PCH2), 3.87−3.97 (m, 2H, CH2Cl), 5.26 (dm, JHP = 330.0 Hz, 2H,
2
Isomer A. 31P NMR (CH2Cl2): δ −20.4 (1JPW = 157.8 Hz, JPW
=
PH). 13C NMR (CDCl3): δ 10.86 (dd, JCP = 15.4 Hz, J = 3.9 Hz CH2),
17.46 (dd, JCP = 17.6 Hz, J = 2.2 Hz CH2), 31.50 (dd, JCP = 12.1 Hz, J
= 6.6 Hz CH2P), 41.53 (pseudo-t, JCP = 5.5 Hz, CH2Cl), 194.41−
194.63 (m, CO cis), 196.54 (d, JCP = 25.6, CO trans).
1
1
70.2 Hz). H NMR (CDCl3): δ 6.38 (d, JHP = 342.9 Hz, 2H, PH),
7.34−7.56 (m, 10H, Ph). 13C NMR (CDCl3): δ 129.72 (pseudo-t, JCP
= 4.1 Hz, C meta), 130.07 (pseudo-t, JCP = 18.0 Hz, C ipso), 131.94 (s,
C para), 133.07 (pseudo-t, JCP = 6.8 Hz, C ortho), 194.91 (pseudo-t,
Diphosphirane 6. A solution of 7-phosphanorbornadiene complex
1d (1.29 g, 2 mmol), borane−triphenylphosphine complex (1.11 g, 4
mmol) and CuCl (79 mg, 0.8 mmol) in THF was stirred at 60 °C for 4
h. Then, an excess of aqueous K2CO3 (0.24 mol/L) was added to the
reaction mixture at room temperature. The reaction mixture was
stirred at room temperature for 30 min. THF was removed by rotary
evaporator. The aqueous phase was extracted with CH2Cl2 three times.
The organic layer was dried with magnesium sulfate, filtered, and
concentrated by rotary evaporator. The residue was chromatographed
on silica gel using a 10/1 petroleum ether/dichloromethane mixture,
to give 6 as a yellowish solid (417 mg, 54%). For the NMR data, see
ref 8.
JCP = 2.3 Hz, CO cis), 197.24 (pseudo-t, JCP = 12.8 Hz, CO trans).
2
Isomer B. 31P NMR (CH2Cl2): δ −23.5 (1JPW = 161.2 Hz, JPW
=
1
1
64.2 Hz). H NMR (CDCl3): δ 6.39 (d, JHP = 350.1 Hz, 2H, PH),
7.34−7.56 (m, 10H, Ph). 13C NMR (CDCl3): δ 128.16 (pseudo-t, JCP
= 17.8 Hz, C ipso), 129.35 (pseudo-t, JCP = 4.1 Hz, C meta), 131.68 (s,
C para), 133.76 (pseudo-t, JCP = 6.6 Hz, C ortho), 195.16 (pseudo-t,
JCP = 2.3 Hz, CO cis), 197.43 (pseudo-t, JCP = 12.8 Hz, CO trans).
Diphosphine 2b. A solution of 7-methyl-7-phosphanorbornadiene
complex 1b (824 mg, 1.5 mmol), borane−triphenylphosphine
complex (825 mg, 3 mmol), and CuCl (58 mg, 0.6 mmol) in THF
was stirred at 60 °C for 2 h. After evaporation, the residue was
chromatographed on silica gel using a 6/1 petroleum ether/
Diphospholane 7. Aqueous K2CO3 (2 mL, 0.4 mol/L) was added
dropwise to a solution of secondary diphosphine complex 2a (112 mg,
0.13 mmol) and BrCH2CH2CH2Br (18 μL, 0.17 mmol) in THF (3
mL). The mixture was stirred at room temperature for 5 h. THF was
removed by a rotary evaporator. The aqueous phase was extracted
three times with CH2Cl2. The organic layer was dried with magnesium
sulfate, filtered, and concentrated. The residue was chromatographed
on silica gel using a 5/1 petroleum ether/dichloromethane mixture, to
give a yellowish solid (57 mg, 48%).
dichloromethane mixture, to give a yellowish solid (144 mg, 26%).
2
Isomer A. 31P NMR (CDCl3): δ −61.5 (1JPW = 159.4 Hz, JPW
=
1
65.1 Hz). H NMR (CDCl3): δ 1.89−2.06 (m, 6H, Me), 5.57 (dm,
1JHP = 336.6 Hz, 2H, PH). 13C NMR (CDCl3): δ 12.73 (pseudo-t, JCP
= 13.1 Hz, Me), 195.03 (q, JCP = 2.3 Hz, CO cis), 197.06 (pseudo-t,
JCP = 13.1 Hz, CO trans).
2
Isomer B. 31P NMR (CDCl3): δ −66.3 (1JPW = 165.0 Hz, JPW
=
59.8 Hz). 1H NMR: δ 1.89−2.06 (m, 6H, Me), 5.59 (dm, 1JHP = 336.6
Hz, 2H, PH). 13C NMR (CDCl3): δ 10.21 (pseudo-t, JCP = 14.3 Hz,
Me), 195.03 (q, JCP = 2.3 Hz, CO cis), 197.06 (pseudo-t, JCP = 13.1
Hz, CO trans).
Compound 7. 31P NMR (CH2Cl2): δ 14.5 (1JPW = 156.5 Hz, 2JPW
=
2
89.7 Hz), 22.9 (1JPW = 155.6 Hz, JPW = 84.7 Hz).
One of the two isomers was purified by recrystallization (hexane
Diphosphine 2c. A solution of 7-thiophenyl-7-phosphanorborna-
diene complex 1c (657 mg, 1 mmol), borane−triphenylphosphine
complex (552 mg, 2 mmol), and CuCl (40 mg, 0.4 mmol) in THF was
stirred at 60 °C for 4 h. After evaporation, the residue was
chromatographed on silica gel using a 10/1 petroleum ether/
and dichloromethane).
2
1
31P NMR (CDCl3): δ 22.6 (1JPW = 155.6 Hz, JPW = 84.7 Hz). H
NMR (CDCl3): δ 2.42−2.59 (m, 4H), 3.01−3.08 (m, 2H), 7.46−7.57
(m, 6H, Ph), 7.63−7.68 (m, 4H, Ph). 13C NMR (CDCl3): δ 25.98
(pseudo-t, JCP = 3.8 Hz, CH2), 32.82 (pseudo-t, JCP = 12.1 Hz, CH2P),
129.35 (pseudo-t, JCP = 4.5 Hz, C meta), 131.03 (s, C para), 131.45
(pseudo-t, JCP = 6.8 Hz, C ortho), 133.80 (pseudo-t, JCP = 15.8 Hz, C
dichloromethane mixture, to give a yellowish solid (96 mg, 22%).
1
Isomer A. 31P NMR (CDCl3): δ −35.6 (JPH = 355.0 Hz, JPW
=
162.0 Hz, 2JPW = 75.0 Hz). 1H NMR (CDCl3): δ 6.83 (d, 1JHP = 360.6
Hz, 2H, PH), 7.27 (t, J = 3.9 Hz, 2H, Th), 7.36−7.41 (m, 2H, Th),
7.78 (d, J = 4.8 Hz, 2H, Th). 13C NMR (CDCl3): δ 128.48 (pseudo-t,
JCP = 16.1 Hz, C), 129.41 (q, JCP = 4.5 Hz, CH), 134.74(s, CH),
138.65 (pseudo-t, JCP = 7.0 Hz, CH), 194.66 (pseudo-t, JCP = 2.0 Hz,
ipso), 195.76 (pseudo-t, JCP = 3.0 Hz, CO cis), 197.94 (pseudo-t, JCP
12.8 Hz, CO trans).
=
HRMS: calcd for C25H16O10P2W2 [M]+ 905.9237, found 905.9235.
ASSOCIATED CONTENT
CO cis), 196.83 (pseudo-t, JCP = 13.4 Hz, CO trans).
■
1
Isomer B. 31P NMR (CDCl3): δ −44.5 (JPH = 354.9 Hz, JPW
=
S
* Supporting Information
168.4 Hz, 2JPW = 68.3 Hz). 1H NMR (CDCl3): δ 6.83 (d, 1JHP = 360.6
Hz, 2H, PH), 7.18 (t, J = 4.2 Hz, 2H, Th), 7.36−7.41 (m, 2H, Th),
7.72 (d, J = 4.8 Hz, 2H, Th). 13C NMR (CDCl3): δ 126.68 (pseudo-t,
JCP = 17.9 Hz, C), 129.41 (q, JCP = 4.5 Hz, CH), 134.74(s, CH),
CIF files giving X-ray data for 2c and 7 and figures giving NMR
spectra of all the compounds described. This material is
available free of charge via the Internet at http://pubs.acs.org.
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Note
AUTHOR INFORMATION
Corresponding Authors
*E-mail for R.T.: tianrq@zzu.edu.cn.
*E-mail for Z.D.: duanzheng@zzu.edu.cn.
*E-mail for F.M.: fmathey@ntu.edu.sg.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(Nos. 21072179, 21272218), the Scientific Research Founda-
tion for the returned overseas Chinese, Zhengzhou University,
and Nanyang Technological University in Singapore for
financial support of this work.
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